From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: Re: [v6 2/4] mm, oom: cgroup-aware OOM killer Date: Fri, 25 Aug 2017 11:39:51 +0100 Message-ID: <20170825103951.GA3185@castle.dhcp.TheFacebook.com> References: <20170823165201.24086-1-guro@fb.com> <20170823165201.24086-3-guro@fb.com> <20170824114706.GG5943@dhcp22.suse.cz> <20170824122846.GA15916@castle.DHCP.thefacebook.com> <20170824125811.GK5943@dhcp22.suse.cz> <20170824135842.GA21167@castle.DHCP.thefacebook.com> <20170824141336.GP5943@dhcp22.suse.cz> <20170824145801.GA23457@castle.DHCP.thefacebook.com> <20170825081402.GG25498@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=facebook; bh=p5yyu4yu9sEA+6iZ5kqwK3jvUAIGUZKz1F6Qb4a/V6I=; b=hhYq4MNdAYmWNlhnDNfXMHyy2hpsbVnjTN+1zymgJPs2O+gW53CmdPA0mnywfspJyvPU 9E6rVVqHgNwnXhFnX1gb21Qe/VT6iXJKQ2H36plWheHSAU63YMjqVqrle4uizgmYpbCe nVwpyDWplKNhAzfKWIQuyheSd4szuTerMrw= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector1-fb-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=p5yyu4yu9sEA+6iZ5kqwK3jvUAIGUZKz1F6Qb4a/V6I=; b=Bjbcc8PXQMLFEo/OlIP3ydoYYIPGDFDYB162lwFxUNwaz9QDijp+I35uM7uI8tXFSP7+IXoGZmVtUOQNFiS/X/l6YDRpwq9vVNReWil22CpoMP60DNenzdH+mcUXj1FsM2c4mclzMAmVLYuhr6fSGf+2XyIOS9JUqBsmtCE44NY= Content-Disposition: inline In-Reply-To: <20170825081402.GG25498@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: linux-mm@kvack.org, Vladimir Davydov , Johannes Weiner , Tetsuo Handa , David Rientjes , Tejun Heo , kernel-team@fb.com, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org On Fri, Aug 25, 2017 at 10:14:03AM +0200, Michal Hocko wrote: > On Thu 24-08-17 15:58:01, Roman Gushchin wrote: > > On Thu, Aug 24, 2017 at 04:13:37PM +0200, Michal Hocko wrote: > > > On Thu 24-08-17 14:58:42, Roman Gushchin wrote: > [...] > > > > Both ways are not ideal, and sum of the processes is not ideal too. > > > > Especially, if you take oom_score_adj into account. Will you respect it? > > > > > > Yes, and I do not see any reason why we shouldn't. > > > > It makes things even more complicated. > > Right now task's oom_score can be in (~ -total_memory, ~ +2*total_memory) range, > > and it you're starting summing it, it can be multiplied by number of tasks... > > Weird. > > oom_score_adj is just a normalized bias so if tasks inside oom will use > it the whole memcg will get accumulated bias from all such tasks so it > is not completely off. I agree that the more tasks use the bias the more > biased the whole memcg will be. This might or might not be a problem. > As you are trying to reimplement the existing oom killer implementation > I do not think we cannot simply ignore API which people are used to. > > If this was a configurable oom policy then I could see how ignoring > oom_score_adj is acceptable because it would be an explicit opt-in. > > > It also will be different in case of system and memcg-wide OOM. > > Why, we do honor oom_score_adj for the memcg OOM now and in fact the > kernel memcg OOM killer shouldn't be very much different from the global > one except for the tasks scope. Assume, you have two tasks (2Gb and 1Gb) in a cgroup with limit 3Gb. The second task has oom_score_adj +100. Total memory is 64Gb, for example. I case of memcg-wide oom first task will be selected; in case of system-wide OOM - the second. Personally I don't like this, but it looks like we have to respect oom_score_adj set to -1000, I'll alter my patch. > > > > > I've started actually with such approach, but then found it weird. > > > > > > > > > Besides that you have > > > > > to check each task for over-killing anyway. So I do not see any > > > > > performance merits here. > > > > > > > > It's an implementation detail, and we can hopefully get rid of it at some point. > > > > > > Well, we might do some estimations and ignore oom scopes but I that > > > sounds really complicated and error prone. Unless we have anything like > > > that then I would start from tasks and build up the necessary to make a > > > decision at the higher level. > > > > Seriously speaking, do you have an example, when summing per-process > > oom_score will work better? > > The primary reason I am pushing for this is to have the common iterator > code path (which we have since Vladimir has unified memcg and global oom > paths) and only parametrize the value calculation and victim selection. I agree, but I'm not sure that we can (and have to) totally unify the way, how oom_score is calculated for processes and cgroups. But I'd like to see an unified oom_priority approach. This will allow to define an OOM killing order in a clear way, and use size-based tiebreaking for items of the same priority. Root-cgroup processes will be compared with other memory consumers by oom_priority first and oom_score afterwards. What do you think about it? Thanks! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org